This invention relates to hair dye compositions having excellent dyeing properties for hair and good fastness to shampoo without causing staining to the scalp or skin.
Acidic hair dye compositions with various organic solvents, typified by benzyl alcohol, contained as penetrant solvents (JP 61-210023 A, JP 7-101841 A, etc.) involve a problem in that upon dyeing, they tend to stain the scalp and skin at the same time, although their penetration into hair is good.
It has, therefore, been a conventional practice to thicken these compositions with a water-soluble high-molecular substance or the like such that they are prevented from dripping or running o f to reduce staining to the skin. This conventional practice is, however, still unable to bring about any substantial solution to the problem (JP 10-87450 A, JP 9-255540 A, JP 8-245348 A, etc.). It has also been proposed to lower the skin staining tendency with an aromatic alcoholic compound, a lower alkylene carbonate or the like (JP 10-53970 A, JP 48-23911 B). This approach, however, cannot bring about sufficient effects either.
With the foregoing circumstances in view, the present assignee developed an acidic hair dye composition having excellent dyeing properties for hair and good shampoo fastness with a reduced tendency of staining to the skin by adding a lower alkylene carbonate as a penetrant solvent and also adjusting the buffer capacity of the composition to a specific range (JP 2000-186018 A).
As the lower alkylene carbonate undergoes hydrolysis in an acidic range and gives off carbon dioxide, packaging of the acidic hair dye composition in a container of the closed system leads to problems such as bulging of the container and leakage of liquid upon application. It is hence required to provide the container with a special means such as a vent.
An object of the present invention is, therefore, to provide a hair dye composition, which has low staining tendency to the skin and excellent dyeing properties for hair and does not give off gas through hydrolysis even in an acidic range.
The present inventors have now found that an acidic hair dye composition, which has low staining tendency to the skin, excellent dyeing properties for hair and good shampoo fastness and does not give off gas through hydrolysis even in an acidic range, can be obtained when a 5-membered or 6-membered cyclic lactone compound is added as a penetrant solvent and the buffer capacity of the composition is adjusted to a particular range.
The present invention, therefore, provides a hair dye composition comprising the following ingredients (A) and (B):
(A) a compound having a 5- or 6-membered lactone skeleton, and
(B) an acid dye; and
having a pH of from 2 to 6 and a buffer capacity not lower than 0.004 gram equivalent/L but lower than 0.2 gram equivalent/L as measured in a form of a tenfold dilute aqueous solution.
The present invention also provides a method of dyeing hair, which comprises applying the above-described hair dye composition onto the hair.